Mixing device



,1969 v G. HUGLI 3,460,811

MIXING DEVICE Filed Nov. 30, 1967 2 Sheets-Sheet 1 Aug. 12, 1969 MGJHU'GLII 3,460,811

MIXING DEVICE Filed Nov. 30. 1967 2 Sheets-Sheet 2 d d e United StatesPatent US. Cl. 259-97 6 Claims ABSTRACT OF. THE DISCLOSURE Apparatus formixing materials including a cylindrical 3,460,231 1 Patented Aug. 12,1969 sleeve will coincide with the axis of the device. However, it isalso possible to arrange said axis at an angle and/or to shift it withrespect to the impeller axis.

For certain applications, the two communicating com- 5 partments of thedevice can be arranged side by side or housing with a coaxialcylindrical jacket disposed therein to form an inner chamber and anouter chamber, an impeller disposed in the inner chamber, and aplurality of baffles disposed in the outer chamber to define a pluralityof flow paths having varying cross sectional areas throughout the outerchamber.

This invention relates to an improved mixing apparatus particularlysuitable for the mixing of viscous liquids.

Conventional mixers using agitators and stirrers are frequently not ableto produce a satisfactory mixing action in highly viscous liquids.

It is known to use built-in annular arrangements such as encasedpropellers to improve the performance of such stirrers. Even then, themixing effect remains unsatisfactory because either the flow speed istoo low or there is to little forced rotary motion of the contents.

It is, therefore, a principal object of the invention to provide amixing device which improves the mixing effect, particularly in viscousliquids.

Other objects and advantages will be apparent from a consideration ofthe specification and claims.

The mixer according to the invention contains a cylindrical jacket whichdivides the inner space into two communicating compartments whereby saidjacket is on its inner face provided with longitudinal bafiles andsurrounds an impeller producing vertical flow. In the space between saidjacket and the outer wall of the tank, there are provided either atleast one vertical baffle and at least one inclined batfle, or at leasttwo inclined baflles in order to produce a large speed gradient and highspeeds.

The portions of the fluid flowing around the edge of the propellerjacket where said portions are not subjected to the action of thedividing baffles and flow at high but widely differing speeds, aresubjected to high shearing stresses and pressure drops which produce avery intensive blending of said portions.

Due to the built-in guiding means, the forced flow, which provides for amixing effect independent of the impeller, can be maintained in allsections of the device even for liquids of very high viscosity; this isnot possible in conventional mixing devices.

The cross-sectional ratio of propeller compartment to jacket compartmentis preferably in the range of 1.5:1 to 5:1.

The number of deflecting baffles disposed in the interspace between theouter wall and the jacket is chosen with advantage so as to provide atleast one inclined baffle in addition to two vertical baflies or only atleast two inclined bafiies. Preferably, two to nine bafiles will beprovided. An excessive number of baffles increases the frictionallosses.

The slope of the inclined baffles is preferably in the range of 15 to 45to the vertical.

Normally, the axis of the cylindrical inner jacket or one behind theother.

The device of the invention is particularly suitable for viscous liquidssuch as solutions of high molecular polymers, fertilizers, and the like.

An illustrative embodiment of the device of the invention is shown, byway of example, in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a mixing device according to the inventionshowing the arrangement of the impeller, inner jacket, and baflies;

FIG. 2 shows the arrangement of the various bafiles with respect to theinner jacket in top view, side view, and as development of the jacket;and

FIG. 3 is a perspective view of the mixer.

Referring to the drawings, an inner cylindrical sleeve 11 divides thecross-sectional area of the mixer in the proportion of 3 (inside):1(outside). An impeller b produces between vertical deflecting bames c astrong current of preferably 0.5-6 m./sec. in vertical direction insidesaid sleeve. The outer ring space is divided by three deflecting bafiiesinto three zones or flow paths through which the materials to be mixedmoves in parallelly divided flows; two of the bafllles d are verticalwhile one baflie c is inclined to the vertical by an angle of 15 to 45In this way, the liquid is divided into flow paths of three diflierentspeeds.

The different speeds or flow rates in the flow paths cause intensivemixing at the top and bottom of the jacket where the flow pathscommunicate due to high speed gradients and shearing stresses, andintensive mixing occurs in the outer ring space or chamber due to thevarying cross sectional areas of the flow paths defined by onelongitudinal baflle d and inclined bafiie e which are skewed withrespect to each other.

EXAMPLE A mixing tank of 450 liter capacity and an outer diameter of 940mm. contained an inner cylinder of 700 mm. diameter which was providedwith two outwardly projecting vertical baffles of about mm. width and athird outwardly projecting baffle which is inclined at an angle of 30 tothe vertical. Said baffles extended over the entire length of thejacket. The three-bladed propeller had a diameter of 550 mm.

The mixer was used for the decomposition of a raw phosphate with nitricacid at a temperature of 50-56 C. 1500 kg./hour of raw phosphate and41.00 kg. of 58% nitric acid were continuously passed through the mixerwhereby the products were introduced near the bottom of the mixer bymeans of a dip tube and the acidulated mixture was drawn off through alateral outlet provided below the upper edge of the stirrer. The speedof the propeller was 220 r.p.m. The viscosity of the produced mesh was10-60 poise (non-Newtonian liquid). The mixer was operated for more than3 months without interruptions.

To obtain the same effect with a conventional mixer, such mixer musthave a capacity of about 5000' liter, and material strongly adheres tothe walls, requiring frequent stoppages for cleaning.

I claim:

1. Apparatus for mixing materials comprising a cylindrical housing, acylindrical jacket having an inner surface and an outer surface anddisposed ,within said housing to form an inner chamber defined by theinner surface of said jacket, and an outer chamber communicating withsaid inner chamber and defined by said housing and the outer surface ofsaid jacket;

an impeller disposed in said inner chamber for causing materials to bemixed to flow through said inner chamber and said outer chamber; and

a plurality of baffles disposed in said outer chamber to define aplurality of flow paths through said outer chamber, said plurality ofbaflies including a pair of adjacent baflies skewed with respect to eachother such that the cross sectional area of a first flow path definedbetween said adjacent baflies varies throughout said outer chamberwhereby intensive mixing of materials occurs in said outer chamber.

2. The invention as recited in claim 1 wherein said pair of adjacentbafiies includes a first bafile disposed in longitudinal alignment withsaid jacket and a second bafiie disposed at an incline to said firstbaffie.

3. The invention as recited in claim 2 wherein said plurality of bafflesincludes a third bafile arranged in parallel with said first baffie todefine a second flow path through said outer chamber between said firstbafiie and said third baflie and a third flow path through said outerchamber between said second baflie and said third bafiie, said thirdflow path having a cross sectional area varying throughout said outerchamber, whereby intensive mixing of materials occurs where said firstflow path, said second flow path and said third flow path communicatedue to diflFerent flow rates in the flow paths.

4. The invention as recited in claim 3 wherein said jacket and saidhousing are coaxial.

5. The invention as recited in claim 3 wherein said second baffle has anincline of from 15 to 45 with respect to said first baflie.

6. The invention as recited in claim 3 wherein the ratio between thecross sectional area of said inner chamber and the cross sectional areaof said outer chamber is in the range of 1.5:1 to 5:1.

References Cited UNITED STATES PATENTS 1,255,944 2/1918 Stevens 259971,701,164 2/1929 Shafor 25997 2,390,460 12/1945 Presser 25997 2,530,81411/1950 Becze 25997 X ROBERT W. JENKINS, Primary Examiner

